This invention relates to a reactor for a continuous gasification of coal under superatmospheric pressure and at elevated temperatures with gaseous gasifying agents which contain free oxygen and with oxygen-free gasifying agents such as water vapor and/or carbon dioxide, comprising a substantially conical grate which is rotatably mounted in the lower portion of the reactor housing (rotary grate) and serves for feeding the gasifying agent and/or discharging the gasification residues.
It has been found that difficulties arise in such gas producers under certain operating conditions in connection with the discharge of the ash from the gas-producing space. Particularly under partial-load conditions, an irregular behavior occurs, which may have the result, e.g., that a reduction of the speed of the grate in proportion with the load is by no means accompanied by a corresponding reduction of the ash discharge rate, which may be either too high or too low, depending on the design of the grate. Additional influences, such as the height of the ash bed, the state of the ash, and the composition of the gasifying agents are significant. This may necessitate intermittent additional steps for removing the ash from the grate plane of the gas producer. In case of difficulties of that kind, a great attention and high qualification are required on the part of the operators so that they can recognize the position and state of the ash bed in the gas producer.
Disturbances in operation arise also, e.g., in case of change of the composition of the ash and a resulting change of its melting and sintering behavior. In known gas producers this also influences the ash discharge rate so that the gas production rate and the composition of the product gas are affected too. If additional means are provided to avoid a retention of ash and this results in a withdrawal of ash at an excessive rate, the core portion of the coal bed may descend too close to the grate. As this core of the coal bed is at the highest temperatures (above 800.degree.C.), a local overheating and destruction of the grate may result. The difficulties involved in the correct adjustment of the grate sometimes cause also an unequal distribution of the gasifying agents emerging from the grate so that existing irregularities, such as an inclination of the ash bed, may be intensified although this is not desired. Such phemomena may result in a unintended decrease of the output of the gas producer for hours and in a steep rise of the content of unburnt coal in the ash. On the other hand, the carbon dioxide content in the product gas increases compared to its combustible constituents.
Changes in design which have been adopted in the past have not basically improved the situation because they have changed also the flow behavior of the ash. When the cross-section of flow of the ash was decreased, larger lumps of ash or an accumulation of sintered ash particles resulted in a clogging whereas in case of an increased flow area in conjunction with a high gas production rate a large amount of the material to be gasified suddenly flowed down into the ash lock without apparent cause and in spite of a constant speed of the grate.